While many products we use in our lives are made of a single material like solid wood, cotton, or aluminum, more and more are made of composites. A composite is a combination of different materials, called constituents. Composites offer certain performance advantages because the constituents work together to give the resulting object special properties. Most composites are made from two or more constituent materials: a binder, or matrix, which surrounds a reinforcement. Not all composites are the product of modern advanced technology. One common example is concrete. In concrete, cement (the binder) is combined with gravel (the reinforcement).

In deciding to use one material or composite over another, engineers consider many factors, among them strength, weight, corrosion resistance, and cost. Depending on the application, other factors may also matter. In developing the next-generation space capsule, NASA engineers need materials that are strong and lightweight (or technically, less massive) but also highly shapeable and resistant to extreme temperatures and fatigue. Before settling on a solution, these engineers will have conducted multiple tests to ensure that the composite fulfills all of these needs.

While spacecraft are still largely made of metal, NASA has begun investigating alternative materials that fulfill its safety objectives but offer performance advantages. The next-generation Space Shuttle Program for manned space exploration includes a newly designed mission crew module—the part of the spacecraft the astronauts will occupy. The design being evaluated, called a composite crew module, or CCM, is made of a carbon-graphite epoxy resin composite. This means that layers of carbon fiber—a material that is just as strong or stronger than steel, at about one-fifth the mass—with graphite reinforcement will cover an aluminum honeycomb shape. The “sandwich” structure will be coated in epoxy resin and cured, or hardened, in a kind of pressure oven called an autoclave. The resulting module will possess considerable strength and be much lighter than if it were made entirely of aluminum. It will be shaped to fit into the International Space Station when docking in space, and its heat shield, located at the bottom of the module, will also be able to withstand reentry temperatures of 3000°F (1650°C).

Composite materials feature in designs beyond spacecraft. Among the many industries already using them is the auto industry. As you might expect in an era of rising fuel prices, car companies are looking for ways to combine strength with weight reduction to improve fuel efficiency. As a result, many have begun developing designs that feature a carbon-fiber body in place of the usual steel and fiberglass. Because of its high ratio of strength to weight, carbon fiber is also used in a variety of consumer products besides cars, including tennis rackets, golf clubs, fishing rods, and bicycles.

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